When a public communications device such as a cell phone places a 911 or other emergency call, a facility known as a Public Safety Answering Point, or PSAP, responds to the call. The PSAP is responsible for determining the nature of the emergency and engaging the appropriate local public safety service, e.g., police, fire etc. Each PSAP serves a predefined geographic area, and a state or province may include many PSAPs. Thus, when an emergency call is placed by a user agent, that is, the person placing the call, the appropriate PSAP must be quickly determined so that the necessary emergency services may be timely called to action. This PSAP in turn must then determine the location of the user agent in order to render emergency service.
When initiating an emergency call, the user agent will likely embed its surface coordinate or civic formatted location within the call routing message. If the user agent calls from a mobile device such as a cell phone, however, there is a possibility that the user agent's location will change during the time required for the emergency service to respond. Thus, the PSAP may attempt to call the user agent back after termination of the original emergency call, to request an update in the user agent's location. However, the user agent may have directed calls from unknown parties such as the PSAP to a forwarding number or to voicemail. Moreover, the user agent may not trust a previously-unknown entity such as a PSAP. For example, the user agent may suspect that the PSAP is a malicious party who may be attempting to hijack the call flow. Thus, the user agent may decline to furnish its location or other confidential information unless it can authenticate the PSAP.
From the above, there is a need for a system and method to authenticate a call from a PSAP back to a user agent following an emergency call.